Deputy Chief Mark Minichini said that on Sunday night, the students, including two 16-year-old girls, one 17-year-old girl and a 17-year-old boy were on Facebook discussing how they would blow up or set fire to the school. At about 8:30 a.m. today, another student handed a printed copy of the discussion to a vice principal of the school, who alerted police.

The school was evacuated around 11:30 a.m. and students were sent home by Superintendent Deborah Perri, who could not be reached for comment this afternoon.

The Essex County Sheriff's Office Bomb Squad was sent to investigate, and the office's K-9 unit sniffed all of the students lockers, finding no explosives.

The four students are being held at the Belleville police department headquarters and were charged with making terroristic threats, creating a false public alarm and conspiracy, according to Minichini.

"I don't believe they had the ways and means of carrying such a thing out," Minichini said. "But we have to take it seriously, and we took it as seriously as we could."